Including Files and Applets in JSP Pages

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Including Files and

Including Files and Applets in JSP Pages

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• <jsp:include page="…"/>

– Using jsp:include to include pages at request time

• <%@ include file="…" %>

– Using <%@ include %> (the include directive)

to include files at page translation time

– Understanding why jsp:include is usually better than

th i l d di ti

the include directive

– Using jsp:plugin to include applets for the Java

Plug-in (rare!)

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Including Pages at Request

Time: jsp:include

– <jsp:include page="Relative address" />

– To reuse JSP, HTML, or plain text content

– To permit updates to the included content without

changing the main JSP page(s)

– JSP content cannot affect main page:

onl t t of incl ded JSP page is sed

only output of included JSP page is used

– Don’t forget that trailing slash

– Relative URLs that starts with slashes are interpreted p relative to the Web app, not relative to the server root

– You are permitted to include files from WEB-INF

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jsp:include Example: A News Headline Page (Main Page)

…

<BODY>

<TABLE BORDER=5 ALIGN="CENTER">

<TR><TH CLASS="TITLE">

What's New at JspNews com</TABLE>

<P>

Here is a summary of our three

most recent news stories:

<OL>

<LI> <jsp:include page="/WEB-INF/includes/Item1.jsp" />

<LI> <jsp:include page="/WEB-INF/includes/Item2.jsp" /> j p p g / / / j p /

<LI> <jsp:include page="/WEB-INF/includes/Item3.jsp" />

</OL>

</BODY></HTML>

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A News Headline Page,

Continued (First Included Page)

<B>Bill Gates acts humble.</B> In a startling and unexpected development Microsoft big wig

and unexpected development, Microsoft big wig Bill Gates put on an open act of humility

yesterday.

<A HREF="http://www.microsoft.com/Never.html"> More details </A>

– Note that the page is p g not a complete HTML document; it p ; has only the tags appropriate to the place that it will be inserted

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A News Headline Page: Result

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The jsp:param Element:

Augmenting Request Parameters

<jsp:include page="/fragments/StandardHeading.jsp">

<jsp:param name="bgColor" value="YELLOW" />

</jsp:include>

– http://host/path/MainPage.jsp?fgColor=RED

M i

– fgColor: RED

bgColor: null

– bgColor: null

• Included page p g

– fgColor: RED

– bgColor: YELLOW

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Including Files at Page Translation

Time: <%@ include … %>

<%@ i l d fil "R l ti dd " %>

– <%@ include file="Relative address" %>

– To reuse JSP content in multiple pages, where JSP p p g ,

content affects main page

Servers are not required to detect changes to the included

– Servers are not required to detect changes to the included file, and in practice they don’t

– Thus, you need to change the JSP files whenever the included file changes

included file changes

– You can use OS-specific mechanisms such as the Unix

“touch” command, or

• <% Navbar.jsp modified 4/1/09 %>

<%@ include file="Navbar.jsp" %>

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jsp:include vs

<%@ include …>

jsp:include <%@ include …%> Basic syntax <jsp:include page=" " /> <%@ include file=" " %>

When inclusion

occurs Request time Page translation time

occurs What is included Output of page Contents of file

Number of resulting

servlets

Can included page set

response headers that

affect the main page?

Can included page

define fields or methods

that main page uses?

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Does main page need to

be updated when

included page changes?

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Which Should You Use?

– Changes to included page do not require any

manual updates

– Speed difference between jsp:include and the include

– Speed difference between jsp:include and the include directive (@include) is insignificant

• The include directive (<%@ include …%>) ( @ ) has additional power, however

– Main page

• <%! int accessCount = 0; %>

– Included page

• <%@ include file="snippet.jsp" %>

• <%= accessCount++ %>

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Include Directive Example:

Reusable Footers

<%@ page import="java.util.Date" %>

<% The following become fields in each servlet that

results from a JSP page that includes this file %>

<%!

private int accessCount = 0;

private Date accessDate = new Date();

private String accessHost = "<I>No previous access</I>";

%>

<P>

<HR>

<A HREF="http//www.my-company.com/">my-company.com</A> This page has been accessed <%= ++accessCount %>

times since server reboot It was most recently

accessed from

<% H t %> t <% D t %>

<%= accessHost %> at <%= accessDate %>.

<% accessHost = request.getRemoteHost(); %>

<% accessDate = new Date(); %>

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Reusing Footers:

Typical Main Page

…

<BODY>

<TABLE BORDER=5 ALIGN="CENTER">

Some Random Page</TABLE>

<P>

Information about our products and services.

<P>

Blah, blah, blah.

<P>

Yadda, yadda, yadda.

<%@ include file="/WEB-INF/includes/ContactSection.jsp" %>

</BODY></HTML>

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Reusing Footers: Result

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Understanding jsp:include vs

<%@ include … %>

• Footer defined the accessCount field

(instance variable)

• If main pages used accessCount, they

would have to use @include

Otherwise accessCount would be undefined

– Otherwise accessCount would be undefined

• In this example, the main page did not use p , p g accessCount

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Applets and jsp:plugin

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Why Applets?

– When HTML (even with Ajax) cannot support GUI

– Many browsers lack Java support

– Applet programming relatively tediouspp p g g y

• Alternatives

– Consider Flash or even Silverlight instead

– The fact that you are using Java on the server should not make you any more likely to use Java on the client!

jsp:include is very important part of JSP jsp:plugin is not

– jsp:include is very important part of JSP jsp:plugin is not

• Skip this entire tutorial section if you do not plan on using applets

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Options for Deploying Applets

• Support for very old browsers

– Develop the applets with JDK 1.1 or even 1.02

– Have users install any version of the Java 2 Plug-in, then use Java 2 for the applets

• This second option simplified by the jsp:plugin tag

– Have users install version 5 or 6 of the Java Runtime Environment (JRE), then use JDK 1.5/1.6 for the applets.( ), pp

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Using jsp:plugin

– Expands into the real OBJECT and EMBED tags

– <APPLET CODE="MyApplet.class" y pp

WIDTH=475 HEIGHT=350>

</APPLET>

• Equivalent jsp:plugin

– <jsp:plugin type="applet"

code="MyApplet.class"

width="475" height="350"> g

</jsp:plugin>

– JSP element and attribute names are case sensitive

– All attribute values must be in single or double quotes

– This is like XML but unlike HTML

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jsp:plugin: Source Code

<jsp:plugin type="applet"

code="SomeApplet.class"

width="300" height="200">

</jsp:plugin>

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jsp:plugin: Resultant HTML

<object classid=

"clsid:8AD9C840-044E-11D1-B3E9-00805F499D93" clsid:8AD9C840 044E 11D1 B3E9 00805F499D93 width="300" height="200"

codebase="http://java.sun.com/products/plugin/1.2 2/jinst all-1_2_2-win.cab#Version=1,2,2,0">

<param name="java_code" value="SomeApplet.class">

<param name="type" value="application/x-java-applet;">

<COMMENT>

/

<embed type="application/x-java-applet;" width="300"

height="200"

pluginspage="http://java.sun.com/products/plugin/" java code="SomeApplet class"

>

<noembed>

</COMMENT>

</noembed></embed>

</object>

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jsp:plugin: Example

(JSP Code)

…

<BODY>

<CENTER>

<TABLE BORDER=5>

Using jsp:plugin</TABLE>

<P>

<jsp:plugin type="applet"

d "Pl i A l t l "

code="PluginApplet.class"

width="370" height="420">

</jsp:plugin>

</CENTER></BODY></HTML>

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(Java Code)

import javax.swing.* ;

/** An applet that uses Swing and Java 2D

* and thus requires the Java Plug-in q g

*/

public class PluginApplet extends JApplet {

public class PluginApplet extends JApplet { public void init() {

WindowUtilities.setNativeLookAndFeel(); setContentPane(new TextPanel());

}

• Where are class files installed?

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(Result)

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Attributes of

the jsp:plugin Element

• type

– For applets, this should be "applet"

Use "bean" to embed JavaBeans elements in Web pages

– Used identically to CODE attribute of APPLET,

specifying the top-level applet class file p y g p pp

• width, height

– Used identically to WIDTH, HEIGHT in APPLET

– Used identically to CODEBASE attribute of APPLET

li

• align

– Used identically to ALIGN in APPLET and IMG

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Attributes of

the jsp:plugin Element (Cont )

– Used identically to HSPACE, VSPACE in APPLET,

• archive

– Used identically to ARCHIVE attribute of APPLET, specifying a JAR file from which classes and images should be loaded

– Used identically to NAME attribute of APPLET,

specifying a name to use for inter-applet communication

or for identifying applet to scripting languages like

JavaScript.p

• title

– Used identically to rarely used TITLE attribute

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Attributes of

the jsp:plugin Element (Cont )

• jreversion

– Identifies version of the Java Runtime Environment

(JRE) that is required Default is 1.2

• iepluginurl

– Designates a URL from which plug-in for Internet

Explorer can be downloaded Users who don’t already have the plug-in installed will be prompted to download it p g p p from this location Default value will direct user to Sun site, but for intranet use you might want to direct user to a local copy.y

• nspluginurl

– Designates a URL from which plug-in for Netscape can

be downloaded Default value will direct user to Sun site

be downloaded Default value will direct user to Sun site, but for intranet use you might want local copy

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The jsp:param and jsp:params Elements

– <APPLET CODE="MyApplet.class"

<PARAM NAME="PARAM1" VALUE="VALUE1">

<PARAM NAME "PARAM2" VALUE "VALUE2">

</APPLET>

• Equivalent jsp:param q j p p

– <jsp:plugin type="applet"

width="475" height="350">

<jsp:param s >

<jsp:param name="PARAM1" value="VALUE1" />

<jsp:param name="PARAM2" value="VALUE2" />

</jsp:param s >

</jsp:plugin>

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The jsp:fallback Element

– <APPLET CODE="MyApplet.class"

<B>Error: this example requires Java.</B>

</APPLET>

• Equivalent jsp:plugin with jsp:fallback

– <jsp:plugin type="applet" jsp:p ug type app et

width="475" height="350">

<jsp:fallback>

<B>Error: this example requires Java.</B>

</jsp:fallback>

</jsp:plugin>

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Summary

• <jsp:include page="Relative URL" />

– Output of URL inserted into JSP page at request time

– Cannot contain JSP content that affects entire page

Changes to included file do not necessitate changes to

– Changes to included file do not necessitate changes to pages that use it

• <%@ include file="Relative URL" %> @

– File gets inserted into JSP page prior to page translation

– Thus, file can contain JSP content that affects entire page

(e.g., import statements, declarations)

– Changes to included file require you to manually update pages that use it

• <jsp:plugin >

– Simplifies writing applets that use the Java Plug-In

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Questions?

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